Prostheses are typically lightweight components that replace damaged or missing body parts of a particular patient. Prostheses must withstand significant forces applied via complex, variable motions of the surrounding body parts. Additionally, prostheses should desirably fit and move like a natural body part of a patient. Prosthetists, therefore, often custom fit a prosthetic device to correspond to the particular anatomical features and movement of each individual patient.
Prosthetic limbs are one type of prosthesis that involve complex shapes and motions. FIG. 1A is an exploded isometric view of a conventional leg socket 10 that may be attached to a leg stump S of a particular patient P. The socket 10 typically has a lightweight liner 12 composed of a thermoplastic or fiberglass sheet. Because the leg stump S varies from one patient to another, the liner 12 is custom made to fit each patient. The leg socket 10 may also have a connector 20 with a dome 22 and an inverted pyramid 26 projecting from the dome 22. The connector 20 is generally attached to the distal end of the liner 12, and the inverted pyramid 26 is generally configured to engage a mating adapter of a lower leg prosthetic device (e.g., a pylon--not shown).
FIG. 1B is an isometric view of the leg socket 10 in which the liner 12 has a reinforced section 14 with a number of threaded holes 16. The connector 20 accordingly has an annular flange 21 with a number of elongated holes 23 to receive a plurality of bolts 18. The pyramid 26 may project from the dome 22 along the central axis C--C of the connector 20, and the pyramid 26 may have a plurality of flat faces 28 to engage the set screws of an adapter (not shown). In another prior art device shown in FIG. 1C, an off-set connector 20a has a dome 22a and a pyramid 26a positioned along an eccentric axis E--E offset from the central axis C--C of the connector 20a. To attach either of the connectors 20, 20a to the reinforced section 14, a prosthetist threads a number of bolts 18 (FIG. 1B) into the holes 16 of the reinforced section 14 (FIG. 1B).
One important aspect of attaching the connectors to the socket is to position the pyramid at a location corresponding to the natural joint for the missing limb. A prosthetist accordingly takes great care in making the liner 12 and the reinforced section 14 to position the central pyramid 26 of the connector 20 (FIG. 1B) at the natural joint location. In many applications, however, the connector 20 may not locate the central pyramid 26 at the natural joint location because the holes 16 in the reinforced section 14 are not positioned correctly or the liner 12 does not fit on the leg stump (FIG. 1A) as planned. A prosthetist may accordingly attach the off-set connector 20a (FIG. 1C) to the reinforced section 14 to position the off-set pyramid 26a at a location that best approximates the natural joint location.
One drawback of conventional systems is that it is time-consuming to attach a connector to the liner at the natural joint location. For example, the prosthetist may need to try several different off-set connectors with varying offsets to locate the pyramid at the natural joint location. The prosthetist may accordingly assemble and disassemble a prosthesis several times before finding the best connector for a particular patient. Moreover, in some cases, none of the available off-set connectors may accurately locate the off-set pyramids at the natural joint location of a particular patient. In such cases, the patients must not only learn to adapt to a prosthetic device, but they must do so with one that does not fit well or articulate in the best approximation of the natural limb. Therefore, conventional systems are time-consuming to assemble and the final prosthesis may not even fit the particular patient.
Another important aspect of attaching a connector to the reinforced section 14 is to align the faces 28 of the pyramid 26 along axes that provide the most natural articulation of the prosthetic limb. For example, natural knee joints articulate about anterior-posterior and medial-lateral axes, and the orientation of these axes varies from person to person. As such, prosthetists also try to align the pyramid faces 28 with the natural articulation axes of a specific patient. Aligning the pyramid faces 28 with the natural articulation axes of a particular patient, however, may be difficult because the position of the pyramid 26 may prevent accurate alignment of the faces 28. The prosthetist is often left with compromising between locating the pyramid at the natural joint location and aligning the pyramid faces with the natural articulation axes. Thus, conventional connectors may not provide the desired fit or articulation for a particular patient.